(1) Field of the Invention
The invention generally pertains to a fully emptiable flexible tube resistant to stress-cracking and forming a water vapour barrier.
The invention also concerns a method for fabricating said tube.
More precisely, the invention, according to a first characteristic, concerns a fully emptiable tube provided with a wall resistant to stress-cracking and forming a water barrier, this tube essentially comprising a flexible skirt and a head, the skirt being elongate along an axial direction and having, at a first end of the tube, a filling end sealed by crushing this skirt along a transverse direction, and the head comprising at least one evacuation orifice and a flexible neck forming a radial extension of the orifice and being joined to the skirt, at least the skirt and neck forming a single piece assembly, the wall at the joining of the neck and skirt and in a longitudinal plane containing the axial direction and perpendicular to the transverse direction, having a determined joining radius, and the skirt in a plane transversal to the axial direction and at mid-distance between the neck end forming the evacuation opening and the filling end of the tube having a determined perimeter and a substantially constant wall thickness, the ratio of the determined perimeter to the joining radius being no more than 4.5.
(2) Prior Art
A tube of this type is described and illustrated for example in patent EP 1 181 207.
Paste products, such as toothpaste, pharmaceutical products, cosmetic products, food products, hygiene products, fats and greasy substances, putty and glue are often proposed in packaging of flexible tube type. These tubes consist of a tubular body of constant cross-section, before the filling end is sealed, of circular, oval or other shape. The tubular body forming what is called the “skirt” has a first end generally closed by heat sealing and a second opposite end, configured so as to form a dispensing head for the product contained in the skirt. The dispensing head is provided with screw-on, snap-fit or other closing means of so-called “standard” cap type, so-called “service” cap type or other.
As a general rule, heat sealing of the first end of the tube is made after filling the tube with the paste product to be packaged.
The capacity of the tube is one of its essential characteristics. In the particular case of a tube with constant circular cross-section, the capacity is defined by the length and diameter of the skirt, i.e. by the length and diameter of the circular cross-section of the skirt.
To extract the product from the tube, the consumer presses on the tube wall which undergoes deformation and creasing that are increasingly pronounced as and when the tube is emptied.
The tube skirt must therefore be made in a flexible material. This material must be heat sealable. It must also have characteristics of resistance to stress-cracking, imperviousness to water vapour and no yellowing in time under the effect of the products contained in the tube or through so-called “cross” contamination i.e. attributable to contamination agents external to the tube, in order to meet specifications of compatibility of products intended to be packaged in the tube.
Tubes meeting all these criteria are most often fabricated by assembly or insert moulding of the dispensing head made by injection and of the skirt made by extrusion.
Another method, called injection blow moulding, that is little used and costly, consists of forming the skirt by moving the impression of a mould consecutively to injection of the head in this mould.
Finally, at least the skirt and neck may be made by injection in a single operation as indicated in above-mentioned patent EP 1 181 207.
The fabrication of the tube using the injection method offers numerous advantages: this method can replace a succession of operations by a single operation. It chiefly allows great freedom of shape and eliminates the welding between the neck and skirt of the tube which is a rigid zone hence a factor of discomfort for the user.
The injection method combined with a low ratio between the skirt perimeter and the neck joining radius makes it possible to fabricate so-called “fully emptiable” tubes which can be completely emptied of their content by pressing on the, flexible neck.
The industrial production of these tubes in large series has encountered a major problem however, which up until now has considerably slowed down its extent of application, and which derives from the insufficient reversibility even the total lack of irreversibility of the deformation undergone by said fully emptiable tubes when they are being emptied.
This problem, novel by nature, in no way affects conventional tubes whose head has much greater rigidity than the skirt, and all the more since the skirt consists of a developable surface, cylindrical for example.
In this well-known case and illustrated for example in patent EP 0 856 473, the skirt only undergoes deformations that are topologically equivalent to creases and returns to its rest position under the effect of the substantial elastic return force exerted upon it by the head after being arched.
On the other hand, for fully emptiable tubes, and even in cases when the ratio of the skirt perimeter to the neck joining radius is low, preferably less than 4.5, the skirt's return to its initial shape after pinching of the tube neck is largely impeded by the fact that the neck, on account of its spheroid-type shape, undergoes compression tangential to its surface when pinched at every point of the surface on which pressure is exerted.
For a certain configuration of the tube's physical parameters, it may arise that not only the inversion of concavity which the tube neck undergoes in its zone on which most stress is placed on pinching, no longer has to overcome an elastic return force but is itself propagated to the benefit of an elastic force in reverse direction which tends to apply the neck zone undergoing most stress onto that part of the neck which maintains its initial convex shape.